Modeling and simulation of four boreholes heat transfer and intermittent running

In order to simulate and analyze the soil temperature field of borehole groups in different working condition, a four boreholes vertical U-shaped pipe heat transfer model outside the boreholes in cylindrical coordinate is established. Using the Virtual Heat Source and Green function method, based on g-function and the unsteady three-dimensional heat transfer model, the four boreholes model gives out a numerical simulation on the heat transfer process in the case that the soil is isotropic medium with MATLAB. Compared to the experiment the the accuracy of the model is verified. By the simulation results, intermittent running is beneficial to the recovery of soil temperature and small running ratio is better than large one.